Dragless flight control system for flying objects

ABSTRACT

The Dragless Flight Control System for Flying Objects utilizes paired fins that are mounted to rotate in opposite directions. When no lift is desired during the object&#39;s flight, the fins are completely retractable into their housings recessed into the body of the object. This minimizes the drag. The fins are set to a maximum no-stall angle relative to the body axis of the flying object. To provide lift and other flight controls, such as roll and yaw, the fins are selectively exposed outside the exterior skin of the flying object by being rotated on their axes, the two fins in a pair always being rotated in opposite directions. Varying the amount of exposed area of the counter-rotating fins can generate lift effect that is proportional to the exposed area and similar to that produced by current permanently extended standard rotational fins.

DEDICATORY CLAUSE

The invention described herein may be manufactured, used and licensed byor for the Government for governmental purposes without the payment tome of any royalties thereon.

BACKGROUND OF THE INVENTION

At present, no flying objects, such as missiles, utilize dual recessedfins (referred to as “canards” in cases of missiles) to control theirflight.

In cases of missiles, for example, historically the flight control hasbeen achieved by using the current standard rotational canard control.The current canard control typically involves multiple rigidly extendedcanards that are axially rotated about the canard axis, the canard axisbeing normal to the main longitudinal missile axis. Such standardrotational canard control generates large control forces because of the“lift” generated by angling the canards to a desired angle into the airflowing around the missile body during missile flight. But majorlimitations attend this type of control. The most substantial are thecanard drag forces and the consequential limited control authorityafforded during the boost phase of the missile. The drag added by therigidly extended canards impacts the overall missile design, especiallyfor those missiles required to carry large propellant loads because ofthe range to be covered. The currently-used extended-canardconfiguration severely reduces the missile range as well as speed. Incases of hypervelocity missiles, such as Compact Kinetic Energy Missile(C-KEM), the canard drag may nullify altogether the very advantage ofmaneuverability sought by using the canards.

SUMMARY OF THE INVENTION

The Dragless Flight Control System for Flying Objects, referred to asthe DFCS, greatly minimizes drag and, as a result, reduces the totalpower loss suffered by the object during its flight. With the DFCS, dragexists only when the fins are proportionally extended for controlpurposes. When the object is set on its flying course, the fins areretracted completely into the body of the object, thus offering noresistance. Thus, the drag force exerted during the typical period thatthe fins are extended for control purposes is a mere fraction of themaximal drag force exerted by the permanently extended fins.

In DFCS, the retractable fins are mounted in pairs and are set tomaximum no-stall angle 12 relative to axis 11 of flying object 100, themaximum angle being dependent on the operational speeds and the desiredcontrol characteristics of the particular object. The maximum angle ischosen to provide maximum lift over the range of the object's speedswhile avoiding the loss of lift due to the stalling of the fin. The finsare selectively exposable outside exterior skin 8 of the flying objectby being rotated on their axes, the two fins of a pair always beingrotated by the same rotation angle but in opposite directions. Thedegree of fin exposure is determined by the degree of rotation angle,the rotation angle being changeable to vary the portion of the fin beingexposed. Varying the exposed area of the counter-rotating fins cangenerate lift effect that is proportional to the exposed area andsimilar to that produced by the current extended standard rotationalfins. When no lift force is needed, the fins retract into a positionflush with the exterior skin of the flying object, thus offering nodrag.

DESCRIPTION OF THE DRAWING

FIG. 1, views A and B present cross-sectional views of a representativepair of fins, with one fin fully-extended and with both fins retractedbeneath exterior skin 8, respectively.

FIG. 2 depicts a preferred embodiment of the Dragless Flight ControlSystem as it is positioned inside a flying object.

FIG. 3 depicts an alternate embodiment of the Dragless Flight ControlSystem.

FIG. 4 shows yet a third embodiment of the Dragless Flight ControlSystem.

FIG. 5 shows the deployment of several pairs of fins on one flyingobject to control roll and yaw.

FIG. 6 illustrates an effective packaging of multiple pairs of fins bydeploying the pairs in non-linear fashion around the circumference ofthe flying object.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawing wherein like numbers represent like partsin each of the several figures, the structure and operation of the DFCSis explained.

A typical flying object in which the DFCS may be employed is missile 100having body axis 11 that is parallel with the length of the missile anda guidance computer (which may or may not be integral with controller15) that, as a part of its guidance function, issues command signals forthe desired rotational positions of fins 1 and 2. The two fins of a pairare mounted to rest in their respective housings 3 and 16 that arepositioned to be on the same side of missile body axis 11. The housingsare mirrored on that side with axis 11 between them and are recessedinto the body of the missile. Each of the fins has front end 18 and backend 17. In the preferred embodiment of DFCS as depicted in FIG. 2, thefront ends of the fins are closer together than the back ends of thefins. When no lift effect is desired for the missile, the fins arecompletely retracted into their respective housings, thereby exposing nopart outside missile skin 8. When flush with the surface of the missileskin as illustrated in View B of FIG. 1, no fin drag interferes with theaerodynamic properties of the missile's exterior configuration. Whenlift is desired, the fins are selectively exposed through the housingopening such that the movement vector of the fins is normal to the planeof the paper in FIG. 2.

When lift control for the missile flight is desired, an electricalcommand signal indicating the desired fin position is sent from thecomputer to electronic controller 15. The electronic controller alsoreceives information relative to the current fin rotational position.The current fin rotational position may be determined by any suitablemeans, such as by using hall sensors located in drive motor 5. The hallsensors derive the current fin rotational position information bycounting the hall pulses generated by drive motor 5. While other methodsof deriving the current fin rotational position information exist, thehall pulse counting method has the advantage of being able toaccommodate the space and weight constraints of a missile. It is noted,however, that the hall pulse counting method necessitates aninitialization of the fins at the “zero” position to which all otherdetermined positions are held relative. The zero position of the fins isillustrated in View B of FIG. 1. This is the stowed null-effect controlposition. To achieve the optimal operational efficiency of the DFCSduring a flight and give the desired level of missile guidance liftforce, fins 1 and 2 are variably positioned between the extremepositions illustrated in FIG. 1, Views A and B.

Electronic controller 15 which is coupled via wire connector 10 to drivemotor 5 receives the current fin rotational position information fromthe drive motor and compares the information with the desired finposition command signal received from the guidance computer. From thecomparison, an error signal is generated that is representative of acorrective angle and a voltage command corresponding to the correctiveangle. This voltage is translated into rotation of the motor whosetorque is delivered to transmission shaft 14 and, therefrom,simultaneously in opposite directions to both first fin gear shaft 13and second fin gear shaft 19. The result is the rotation of fins 1 and 2in opposite directions until the error signal is eliminated. Thesimultaneous transmission of the torque is accomplished by motor drivegear 7 which is coupled to first fin gear 6 and second fin gear 20. Thefirst fin gear and second fin gear are, in turn, coupled to the firstand second fin gear shafts, respectively. Because of the fins' alignmentto the same motor drive gear 7, the rotation of the motor drive gearresults in the rotation of the fins in mutually opposite directions.Motor transmission 4 “gears down” the rotational speed of the drivemotor and multiplies the torque thereof prior to transmitting the torqueto transmission shaft 14 that rotates motor drive gear 7. The motortransmission can take one of several gearing formats. Two that offeradvantages of large gear ratios and small back lashes are a harmonicdrive and a planetary drive.

The rotational movements of drive motor 5 from the neutral position inresponse to the error signals provides increasing control authority inproportion to the degree of rotational command given to the motor and inaccordance with the rotational direction of the command. A clockwiseerror signal results in a voltage command that energizes the drivingsystem (comprised of drive motor 5, motor transmission 4, first andsecond fin gears 6 and 20, first and second fin gear shafts 13 and 20,motor drive gear 7 and transmission shaft 14) to cause first fin 1 to beexposed outside missile skin 8 by rotating the fin by a pre-determinedcorrective angle while fin 2 is retracted into its corresponding housingby rotating it by the same pre-determined corrective angle. Acounter-clockwise error signal results in a voltage command thatreverses the rotational motions of the fins. With either error signals,the rotation of the fins continues until the error signal is reduced tozero. In all cases, the fins do not rotate beyond a pre-set maximumangle.

FIG. 3 shows an alternate embodiment of the Dragless Flight ControlSystem in which front ends 18 of the fins are further apart from eachother than back ends 17 of the fins. FIG. 4 depicts yet anotherembodiment, that of fins in staggered positions. This positioningrequires a separate motor drive gear for each fin. These alternateembodiments are equally effective in providing the desired actuation andthe ultimate control of the fins and may differ only in their capabilityto meet a given space limitation in the flying object in which the DFCSis to be deployed.

The best effect of DFCS is achieved by using several pairs of the finson one flying object, the pairs deployed at regular intervals from eachother around the circumference of the object. Such a deployment isillustrated in a cross-sectional view of the object in FIG. 5. Matchedfin pairs with fins actuated in parallel angles allow yaw maneuverswhile matched pairs with fins actuated in non-parallel angles allow rollmaneuvers. Further, combinations of different embodiments can beemployed as shown in FIG. 6 for even more versatility.

Although particular embodiments and form of this invention have beenillustrated, it is apparent that various modifications and otherembodiments of the invention may be made by those skilled in the artwithout departing from the scope and spirit of the foregoing disclosure.For example, O-ring seals 9 can be used to seal fin gear shafts 13 and19 rotationally with their respective housings 3 and 16. This permitsavoidance of the external pressures that exist during the flight of theobject. Further, the housings themselves may be sealed to skin 8 toprevent the external pressures from freely entering the flying object'sbody. Additionally, a pneumatic system, instead of direct electricalmanipulation of the fins with electric motors as described above, may beused to introduce the fin pair into the air flow around the flyingobject. With the pneumatic system, the fin pair is introducedproportionally into the air flow in a piston-like arrangement thatallows the fins to slide in a linear fashion into position rather thanrotate into position. Control solenoids regulate the pressure and flowto the fin pistons that alternately position the fin pair at the desiredheight in the air flow. Some of the advantages of such a pneumaticarrangement are greater actuation forces and alternate uses for thepneumatic exhaust, such as driving corresponding thrusters for flightassistance during the transition from launch where fins have littlecontrol authority. On the other hand, disadvantages of the pneumaticsystem include reduced packaging efficiency and increased systemcomplexity due to integration requirements attendant toelectrical/mechanical systems. In accordance with the foregoing, thescope of the invention should be limited only by the claims appendedhereto.

1. A Dragless Flight Control System for controlling the flight of aflying object while minimizing drag, said control system residing insaid object and said object being defined by an exterior skin and havinga guidance computer therein for generating new positional commandsignal, said control system comprising: at least one pair of firsthousing and second housing, said housings being recessed inside saidflying object and each having an opening communicating with saidexterior skin; at least one pair of first and second fins positionedinside said housings, respectively, said fins each having a front endand a back end and being exposable outside said exterior skin and beingcompletely retractable into said housings through said openings, saidfirst and second fins being mounted to rotate in mutually oppositedirections and to have rotation vectors normal to said exterior skin,said fins further being rotatable by variable corrective angles; a meansfor ascertaining current rotational position of said fins; an electroniccontroller coupled between said ascertaining means and said guidancecomputer, said controller generating a signal representative of acorrective angle in response to current rotational position informationfrom said ascertaining means and said command signal from said computer,said controller then further producing a voltage command correspondingto said corrective angle; a drive motor coupled to said electroniccontroller to receive said voltage command and generate a correspondingtorque; a motor drive gear; a motor transmission coupled between saiddrive motor and said motor drive gear to multiply said torqueselectively prior to delivering said torque from said drive motor tosaid motor drive gear; a first fin gear shaft and a second fin gearshaft, said fin gear shafts being rotationally coupled to theirrespective fins so as to allow said fins to rotate; a first fin gearcoupled between said first fin gear shaft and said motor drive gear totransmit said torque from said motor drive gear to said first fin gearshaft to enable said first fin gear shaft to rotate said first fin; asecond fin gear coupled between said second fin gear shaft and saidmotor drive gear to transmit said torque from said motor drive gear tosaid second fin gear shaft to enable said second fin gear shaft torotate said second fin, said first and second fins always rotatingsimultaneously but in opposite directions, thereby exposing one finwhile retracting the other fin until said corrective angle is obtained,thereby achieving desired degree of control of said object's flight. 2.A Dragless Flight Control System as set forth in claim 1, wherein saidcontrol system further comprises two O-ring seals, each seal beingcoupled to one of said fin gear shafts inside its corresponding housingto render stability to said fin gear shaft.
 3. A Dragless Flight ControlSystem as set forth in claim 2, wherein said control system stillfurther comprises a transmission shaft coupled between said motortransmission and said motor drive gear.
 4. A Dragless Flight ControlSystem as set forth in claim 3, wherein said means for ascertainingcurrent rotational position of said fins is a hall sensor located insaid drive motor, said sensor deriving said current rotational positionby counting hall pulses generated by said motor.
 5. A Dragless FlightControl System as set forth in claim 4, wherein said flight controlsystem still further comprises several pairs of said fins, said severalpairs being deployed at regular intervals around the circumference ofsaid flying object.
 6. A Dragless Flight Control System as set forth inclaim 5, wherein said fin gear shafts are positioned to be coupled tosaid front ends of their respective fins.
 7. A Dragless Flight ControlSystem as set forth in claim 6, wherein said fins are positioned withrespect to each other such that said back ends are further apart thansaid front ends.